RECD Installation in Basement DG Rooms: Space and Access Planning

The facility manager of an office tower in Gurugram had approved the purchase order for two retrofit emission control devices. The vendor had sized them, the compliance consultant was satisfied, and the delivery truck was booked. Then the installation supervisor walked the route from the loading dock to the generator room on the second basement level. The ramp was fine. The driveway curve was tight but passable. The trouble started at the last door: a fire-rated double door with a clear opening narrower than the device housing, set below a sprinkler main that left little headroom above it.

Nobody had measured that door. The installation slipped by three weeks while the team argued about removing the door frame, dismantling the housing or bringing it in through a ventilation shaft.

Basement DG rooms are some of the most common generator locations in Indian cities, and some of the hardest places to retrofit. Space is tight, the ceiling is already crowded with services, the exhaust has to climb many floors to reach open air, and every piece of equipment must travel through car parks, ramps and doors that were designed for cars and people rather than steel housings. This guide follows the device on its journey, from the street to the stack, and shows what to measure and decide at each stage.

Why Basements Need Their Own Plan

An RECD in an open yard can usually sit wherever the exhaust pipe happens to run. In a basement, almost nothing is that easy. Four features make basement retrofits different:

• The access route is long and fixed. Equipment must pass through gates, ramps, car park aisles, doors and sometimes lift lobbies, each with its own height and width limit.
• The room is already full. Generators, fuel day tanks, panels, cable trays, fire mains, sprinkler lines and ventilation ducts compete for the same few metres.
• The exhaust has a long vertical run. It usually rises through a dedicated shaft to the terrace or a podium outlet, so the existing backpressure is already significant before any device is added.
• Heat and air have nowhere to go. Every watt that escapes from hot surfaces has to be removed by ventilation fans, and every leak of exhaust stays inside an enclosed space where people work.

Our step-by-step guide to the RECD installation process describes the general sequence. This article focuses on the parts that change when the generator lives underground.

Stage 1: The Journey In

Start the planning at the street, not at the generator. Walk the route the device will take and record every pinch point. A single overlooked beam can stop the installation on delivery day.

What to measure along the route

Point on the route	What to record	Why it matters
Site gate and driveway	Width, height barrier, turning radius	Decides vehicle size and whether a trailer can enter
Ramp to basement	Clear height at the lowest beam, slope, width	Height barriers on ramps are often 2.1 m to 2.4 m
Car park aisles	Lowest beam, sprinkler pipe or duct along the route	Services hang below beam level in many basements
Turns and columns	Distance between columns at each corner	Long housings need room to swing around
DG room door	Clear opening width and height with door leaves fully open	Fire doors often have a smaller clear opening than the frame suggests
Inside the room	Height to the lowest service at the planned device position	Decides whether the device can be lifted into position
Floor	Slab load rating and any trench covers on the route	Pallet trucks and chain blocks concentrate load

Take photographs at each point with a measuring tape visible. Share them with the RECD vendor before the design is frozen, together with nameplate photos of the generator. Our guide to DG nameplate photos for an RECD enquiry explains which photographs help the vendor most.

The three common bottlenecks

The ramp beam. Many basement ramps have a transfer beam at the top or bottom that sets the lowest headroom on the whole route. If the device on its pallet, plus the trolley, exceeds that height, it cannot come down the ramp upright.

The room door. Fire-rated doors often have a fixed centre post, raised thresholds and closers that reduce the clear opening. Removing a door leaf or the centre post may be possible but needs the fire safety team’s agreement and a plan to restore the rating the same day.

The last metre. Inside the room, the device may have to pass between the generator and a wall, under a cable tray or over a fuel line. This is where most last-minute surprises happen.

When the device will not fit through the route

There are several ways around a route that is too small. Each has costs and should be agreed with the vendor in advance.

Option	How it works	Trade-offs
Modular device	Housing supplied in sections and bolted together inside the room	Needs bench space inside the room and careful sealing of joints
Separate filter and catalyst modules	Heavy internal modules delivered separately from the outer shell	Each piece is lighter and smaller, but assembly takes longer
Alternative opening	Use a louvre opening, ventilation shaft or knock-out panel	Needs structural, fire and ventilation sign-off; restoration work
Different device position	Place the device higher up the exhaust route, nearer the terrace	Longer pipe run from the engine, cooler exhaust at the device
Temporary removal of obstructions	Remove a door leaf, centre post, cable tray section or light fittings	Needs permits and same-day restoration

Ask the vendor early whether their design can be split. A device that arrives as one welded piece cannot be made smaller on site.

Stage 2: Finding a Home in the Room

Once the device can reach the room, it needs a place to live. In a basement, the choice is usually between three positions.

Position A: Close to the engine, at floor or low level

The device sits on a stand next to the generator, connected to the turbocharger outlet through a short pipe and a flexible bellows.

• Advantages: hottest exhaust at the device, which helps regeneration; short connection; easy to reach for inspection
• Disadvantages: uses floor area that may not exist; adds a large hot surface at working height; may block walkways or panel fronts

Position B: Overhead, suspended or on a mezzanine frame

The device hangs from the slab or sits on a steel frame above the generator or walkway.

• Advantages: frees floor space; keeps the hot surface away from people
• Disadvantages: the slab or frame must carry the weight plus dynamic loads; access for service needs a platform or ladder; competes with ducts, cable trays and sprinklers

Position C: In or near the exhaust shaft

The device sits at the foot of the riser shaft, sometimes in an adjoining service space, or higher up the shaft at an intermediate floor or the terrace.

• Advantages: keeps the device out of the crowded generator room
• Disadvantages: longer pipe run before the device, so cooler exhaust; harder access for service; a terrace position brings rooftop lifting and structural questions, which our companion guide on rooftop installation covers

Choosing between them

Factor	Position A: low, near engine	Position B: overhead	Position C: shaft or terrace
Exhaust temperature at the device	Highest	High	Lower, especially at the terrace
Floor space used	Most	Least	None in the DG room
Structural work	Floor stand only	Slab anchors or frame	Depends on location
Service access	Easiest	Needs platform	Hardest
Heat added to the room	Most	Moderate	Least
Suitability for light-load sets	Best	Good	Weakest

For most basement rooms with enough floor area, Position A or B gives the best balance. Position C becomes attractive when the room is already full, but the cooler exhaust at a distant device makes regeneration harder for sets that run lightly. Our article on choosing an RECD for a generator running at low load explains why exhaust temperature matters so much.

Stage 3: The Long Climb to Open Air

Basement generators almost always discharge through a vertical shaft. The existing exhaust may already climb 20, 30 or more metres, with several bends on the way. That has two consequences for the RECD.

Backpressure starts high

Every metre of pipe and every bend adds resistance to flow. In a tall building, the existing system may already use a large share of the engine maker’s backpressure allowance before the RECD is added. The device then has to fit into whatever margin is left.

Before ordering, ask for a backpressure calculation for the whole route: engine outlet, bellows, horizontal run, device, bends, riser and terminal. If the margin is thin, options include a larger pipe diameter for part of the route, fewer bends, or replacing the existing silencer with the RECD if noise performance allows. Our articles on how exhaust backpressure affects a DG set and whether an RECD can replace a generator’s exhaust silencer explain the trade-offs.

Heat travels with the pipe

A long riser cools the exhaust. That matters if the device sits high up. It also matters for the building: a hot pipe passing through a shaft lined with other services needs insulation and clearance from anything heat sensitive.

Condensate and rain

Tall exhaust risers collect condensate during cold starts and rain at the top if the terminal is poorly designed. Water running back down the riser can reach the device. Fit a drain point at the base of the riser, use a rain cap or bent terminal at the top and keep the device out of the lowest point where water collects.

Shared shafts

In some buildings, two or more generators share one shaft with separate flues. Each RECD should treat only its own engine’s exhaust. Our article on whether two diesel generators can share one RECD explains why sharing a device is usually a poor idea.

Stage 4: The Heat Budget

An RECD is a large, hot steel box. Even with good insulation, its surface releases heat into the room. In a basement, the ventilation system has to remove that heat along with everything else the generator gives off.

Where the heat comes from

A running generator room already contends with heat from:

• The engine block and exhaust manifold
• The alternator
• The radiator, if it discharges into the room rather than to a duct
• Uninsulated exhaust pipe
• Electrical panels and cables

Adding an RECD inside the room adds surface area at exhaust temperature. Insulation reduces the loss greatly, but rarely eliminates it, especially at flanges, sensor ports and access doors that are often left uninsulated so they can be opened.

Check the ventilation design

Ask the building services team for the room’s design ventilation rate and the allowable temperature rise. Then ask the RECD vendor for the expected surface heat loss with and without insulation. If the margin is small:

• Insulate thoroughly, including removable insulation jackets for flanges and access doors
• Place the device near the exhaust air path, so its heat leaves the room quickly rather than circulating
• Avoid placing it near the engine air intake, where it would warm the combustion air and reduce engine performance
• Consider an upgraded extract fan if measured room temperatures rise after installation

Overheating rooms lead to derating and alarms. Our guides on common causes of generator overheating and summer maintenance tips to prevent generator overheating describe the symptoms to watch for.

Stage 5: Safety Underground

Basement generator rooms bring safety issues that an open yard does not. An RECD installation should improve the room’s safety, not quietly erode it.

Exhaust leaks and carbon monoxide

Every new joint in the exhaust system is a possible leak path. In a basement, leaking exhaust stays in the room and can drift into car parks and stairwells. Diesel exhaust contains carbon monoxide, which gives no warning by smell at dangerous levels; the Wikipedia article on carbon monoxide poisoning outlines the hazard.

• Use proper gaskets and flanges at every joint and check them after the first few heating cycles
• Fit carbon monoxide detection in the room if it is not already present, and link alarms to the building management system
• Test for leaks with the set running at load during commissioning

Fire separation

Generator rooms in basements are normally separated from the rest of the building by fire-rated walls, doors and shafts. Any new penetration for pipes, cables or sensor wiring must be sealed with a fire-rated system. The Bureau of Indian Standards’ guide to using the National Building Code of India 2016 explains how the code’s fire and life safety part is organised. Check with the building’s fire consultant before cutting any opening.

Hot work in an occupied building

Cutting and welding the existing exhaust pipe creates sparks and fumes in a space that may connect to a car park full of vehicles. A hot work permit, fire watch, isolation of smoke detectors only where unavoidable and only for the duration, and ventilation of welding fumes are basic requirements. Our article on whether an RECD can be installed without cutting the existing exhaust pipe describes flange-based approaches that reduce hot work.

Escape routes

The device and its supports must not narrow the room’s exit path or block access to fire extinguishers, emergency stops or fuel shut-off valves. Mark the escape route on the layout drawing before deciding where the device goes.

Confined working

Areas above false ceilings, inside shafts and behind the generator can become cramped work spaces with poor air. Treat them with care, especially during hot work. The general principles of confined space safety are a useful reference.

Stage 6: Planning for Service Day

The device will need inspection, sensor checks and periodic cleaning for its whole life. In a basement, the service visit has to travel the same route as the installation, in reverse, and in a fraction of the time.

Removal path for the filter

Particulate filter modules are removed for ash cleaning. A filter that can be lifted out of its housing but not carried out of the room is not serviceable. Check that:

• The removal direction has clear space at least as long as the module plus room to grip and lift it
• A lifting point or rail exists above heavy modules
• The module, once removed, can travel to the door on a trolley without being tilted beyond what the vendor allows
• The route from the room to the service vehicle is the same one surveyed in Stage 1

Our companion guide on service clearance around an RECD sets out the clearance zones in detail.

Spare module strategy

Cleaning a filter can take days if it goes to a workshop. For buildings that cannot be without backup, a spare filter module swapped in on the same visit avoids downtime. The basement then needs storage for the spare, or the vendor brings it in and takes the dirty one away.

Readings without climbing

Mount the monitoring display or data logger where staff can read it from the floor. A backpressure gauge hidden above a cable tray will not be read. The RECD maintenance guide lists what should be checked and how often.

A Basement Survey Template

Use this template during the site visit. Fill in every line before inviting final quotations.

Item	Record
Generator make, model, kVA and engine power
Number of sets in the room
Room dimensions (L x W x clear height to lowest service)
Floor slab rating, if known
Route from street to room: lowest height point and its location
Route: narrowest width point and its location
DG room door clear opening (W x H)
Existing exhaust route: horizontal length, number of bends, riser height
Existing silencer type and position
Terminal position and type (terrace, podium, side wall)
Ventilation: supply and extract fan ratings, design temperature rise
Radiator type: in-room or ducted
Fire detection and suppression in the room
Carbon monoxide detection present?
Services that cross possible device positions
Escape route and emergency equipment locations
Running pattern: hours per month, typical load

The running pattern matters as much as the dimensions. A basement set that only runs for weekly tests and rare outages behaves very differently from one that runs daily. Our article on whether an RECD suits a DG set that runs only occasionally covers the low-hours case.

Coordinating the People

A basement retrofit touches more teams than most installations. Agree responsibilities before work starts.

Party	Role in the basement retrofit
Building owner or facility manager	Approvals, access windows, communication with occupants
RECD vendor	Device design, route survey, delivery, installation, commissioning
Generator service provider	Engine condition check, isolation, re-commissioning of the set
Building services or MEP consultant	Ventilation, fire separation, structural review of supports
Fire safety officer	Hot work permits, detector isolation, penetration sealing
Security and parking management	Route clearing, vehicle movement, gate access
Tenants or residents	Notice of outages, car park closures and noise

In commercial buildings and malls, tenant coordination often decides the schedule. Our guides on RECDs for shopping malls and RECDs for housing societies describe how to manage occupants during the work.

A Worked Example: Office Tower in Gurugram

Return to the tower from the opening. This is an illustrative case.

The site

• Two 1250 kVA sets on the second basement level, each with its own exhaust riser to the terrace, about 48 metres of vertical run
• DG room 18 m x 11 m, clear height 4.2 m to the slab but only 3.1 m below the lowest cable tray
• Ramp headroom 2.4 m at the transfer beam
• Room door clear opening 1.5 m wide and 2.1 m high after removing the centre post
• Sets run for weekly tests, monthly loaded tests and an average of 25 hours a month of grid outages

What the route survey found

The original device housing, delivered as one piece on a pallet, would have stood at about 2.3 m and measured 1.8 m wide. It would just pass the ramp beam but not the door.

How the problem was solved

1. The vendor supplied each device as three modules: inlet section with catalyst, filter section and outlet section, each under 1.4 m wide.
2. The modules came down the ramp on low trolleys during a Sunday car park closure.
3. Assembly took place inside the room on a temporary bench, with new gaskets at each joint.
4. Each device was mounted overhead on a steel frame spanning between columns beside each generator, clear of the cable trays and with a fixed service platform beneath.
5. The existing silencers stayed in place, because the backpressure calculation showed enough margin once the horizontal run was shortened by 4 metres and two bends were removed.
6. Removable insulation jackets covered flanges and access doors. Room temperature at full load rose by about 2°C compared with the pre-installation test, within the ventilation design margin.
7. Carbon monoxide detection was added and linked to the building management system.
8. A chain hoist rail above each filter module made removal possible without a mobile lifting rig.

What the facility team learned

The extra cost of modular devices and the steel frames was small compared with the three-week delay the original single-piece design would have caused. The service provider now carries out filter changes on the same Sunday window, using a spare module rotated between the two sets. Large sets with demanding duties share many of these issues; see the 1250 kVA DG set RECD page for that rating, and our guide on RECDs for data centres for buildings where testing schedules are tight.

Mistakes That Cost the Most in Basements

Measuring the room but not the route

The room may have space; the route may not. Always walk from the street.

Ignoring services in the ceiling

Clear height to the slab means little if a cable tray or sprinkler main sits half a metre lower. Measure to the lowest obstruction above each possible position.

Treating the riser as free

A tall exhaust riser already consumes backpressure margin. Calculate the whole system, not just the device.

Forgetting the service path

A filter that cannot leave the room cannot be cleaned. Plan the removal path at design stage.

Leaving heat to chance

Insulation, placement and ventilation decide whether the room stays within its design temperature. Check before, not after, the first summer.

Our broader list of common RECD installation mistakes covers errors that apply to every location.

Paperwork and Compliance

Approval for the device itself comes through CPCB’s System and Procedure for Emission Compliance Testing of RECDs. For basement installations, also keep:

• The route survey with photographs and dimensions
• The backpressure calculation for the full exhaust system
• Fire penetration sealing records and hot work permits
• Ventilation checks before and after installation
• Carbon monoxide detector commissioning records

These records help during inspections and when the building changes hands. Our article on what happens during a pollution control board inspection explains what inspectors typically ask to see. For timing, the RECD installation timeline shows how a basement survey fits into the overall programme.

Questions About Basement RECD Installations

Can an RECD be installed in a basement generator room?

Yes. Many basement sets carry RECDs. The key is planning the delivery route, finding a position with enough clearance, checking backpressure on the long exhaust riser and making sure the room’s ventilation can handle the extra heat.

What if the device will not fit through the basement door or ramp?

Ask the vendor for a modular design delivered in sections, or for separate filter and catalyst modules. Other options include using an alternative opening or temporarily removing obstructions with the right permits.

Is it better to mount the RECD near the engine or near the terrace?

Near the engine usually gives hotter exhaust and better regeneration, plus easier service. A terrace position saves room space but cools the exhaust and needs rooftop lifting. The right answer depends on load profile, space and structure.

Will an RECD make the basement DG room hotter?

It adds some heat from its surface. Good insulation, sensible placement near the extract air path and a check of the ventilation design normally keep the effect small.

Do I need carbon monoxide detection when adding an RECD in a basement?

It is strongly advisable. New joints are possible leak points, and exhaust leaks in enclosed spaces are dangerous. Detection linked to the building management system gives early warning.

How is the filter removed for cleaning in a basement?

Through a planned removal path with enough clear space, a lifting point or rail above heavy modules, and a trolley route back to the service vehicle. Plan this at design stage.

Plan the Path, Then the Device

A basement RECD project succeeds or fails on details that have nothing to do with emission chemistry: a beam on the ramp, a door post, a cable tray, a fan rating. Walk the route, measure the room to its lowest obstruction, calculate the whole exhaust system, budget the heat, protect the escape routes and plan the service path before the purchase order is final. Do that, and the device that arrives on delivery day will go straight to the place it was designed for.

Aceget surveys basement routes and rooms as part of every RECD proposal, and supplies CPCB type-approved devices, including modular designs, for engines from 25 kVA to 2500 kVA. To arrange a basement survey, contact Aceget, or browse ratings on the retrofit emission control device page.